1. Field of the Invention
This invention relates to the use of 3-amino-5-alkyl-1,2,4-triazoles as silver protectors in machine dishwashing detergents and to dishwashing detergents containing 3-amino-5-alkyl-1,2,4-triazoles as silver protectors.
2. Discussion of the Related Art
In recent years, low-alkaline machine dishwashing detergents have been available to an increasing extent. Apart from their many advantages, however, the often inadequate protection of silver afforded by these products is a major problem which has pre-occupied both developers and users. Various proposals have been put forward in the more recent patent literature as to how silver can be protected against tarnishing, discoloration, oxidation or other optical and material-related disadvantages.
Thus, redox-active inorganic and organic substances have been described as silver protectors for addition to the wash liquor as have substances which are deposited as a protective layer on the silver surface and special bleaching systems which attack the silver surface to a reduced extent.
One objective of the various developments has been to find substances which are effective in small quantities because this reduces costs.
The use of 3-amino-5-alkyl-1,2,4-triazoles as a corrosion inhibitor for non-ferrous metals is known from DE 29 34 461.
WO-A-95/10588 describes 1,2-N-azoles, preferably imidazole, benzimidazole, tetrazole, 5-aminotetrazole, 1,2,4-triazole, 3-amino-1,2,4-triazole, and histidine as silver protectors which are said to be effective in quantities of 0.05 to 10% by weight in low-alkaline machine dishwashing detergents.
However, neither of the documents cited above discloses the use of 3-amino-5-alkyl-1,2,4-triazoles or mixtures thereof as silver protectors effective in small quantities in machine dishwashing detergents, particularly in low-alkaline machine dishwashing detergents.
The problem addressed by the present invention was to provide a silver protector for machine dishwashing detergents which, in use, would not affect--or would even improve--the performance properties otherwise typical of machine dishwashing detergents, such as cleaning performance, adequate foaming capacity, easy handling and the like, and which would be effective in small quantities.